The present invention relates to compressed gas in situations where, in utilizing the potential energy of the compressed gas through pneumatic devices, it is preferable to recover the gas exhausted from the pneumatic device, including, but not limited to, natural gas production facilities and wells. The present invention also relates to the injection of liquids into compressed gas.
In many situations it is necessary to utilize the potential energy of a compressed gas to power pneumatic devices so as to drive equipment. Pneumatic devices are devices which operate by converting the potential mechanical energy of a compressed gas into motion. Pneumatic devices utilize the tendency of gases to flow from an area of higher pressure to an area of lower pressure and therefore they require a pressure differential in order to operate. Typically, this pressure differential is between the exterior of the pneumatic device, typically the atmosphere, and a supply of gas at a higher than atmospheric pressure, which is fed into the interior of some of the components of the pneumatic device.
In general terms, the components of a pneumatic device may be divided into pressure differential components and non-pressure differential components. The pressure differential components are those components of a pneumatic device which face a pressure differential between their interiors and exteriors during normal operation. Examples of pressure differential components include: pipes and other forms of gas conduits; pneumatic cylinders; and valves. Non-pressure differential components are those components of a pneumatic device which do not face a pressure differential between their interiors and exteriors during normal operation. Examples of non-pressure differential components include: power output means such as shafts; and switch linkages.
In natural gas production facilities, it is often necessary to periodically or continually inject liquids into a high pressure gas pipeline. An example is methanol, which may be injected to prevent any water present in the natural gas from freezing. Such liquids are injected by means of pumps which overcome the pressure of the compressed gas to force the liquid into the pipeline. These injection pumps are often powered by pneumatic devices, particularly in remote locations. In some situations, the compressed gas flowing in the pipeline is used to drive the pump, but typically, only after it has been regulated down to a pressure suitable for the pneumatic device, often around 10 pounds per square inch. The exhaust gas from the pneumatic device comes out of the device at a lower pressure than the gas in the pipeline, so it can""t be reinjected into the pipeline unless it is first compressed. Therefore the exhaust gas is usually vented to atmosphere. In some situations a gas such as propane is brought to the site, stored in a pressure vessel, and used to drive a pneumatic device. This gas is also vented to atmosphere from the pneumatic device.
This venting of the exhaust gas to atmosphere is a problem because it is a waste of valuable gas and because it raises environmental concerns, particularly in the case of sour gas. A means of utilizing the potential energy of the compressed gas, and of injecting liquids into a high pressure gas pipeline, which does not require venting of the gas is required.
In accordance with the invention, it is found in using pneumatic devices that pressurizing the work environment of a variety of pneumatic devices and containers to the same pressure as the compressed gas with which the devices and containers are associated produces many benefits, including, but not limited to, the emission-free operation of pneumatic devices and the efficient injection of liquids into compressed gases.
In accordance with the invention, if a pressure differential exists within a compressed gas system, in a natural gas pipeline for example, and the working environment of the pneumatic device is pressurized by means of direct contact with that compressed gas in the compressed gas system which is at the lower pressure, and the pneumatic device is driven by compressed gas from that portion of the compressed gas system which is at the higher pressure, then the pneumatic device can operate so as to exhaust gas back into the compressed gas system; and the pressure differential components of the pneumatic device will face a maximum pressure differential between their interiors and exteriors equal to the pressure differential within the compressed gas system, rather than the pressure differential between the compressed gas system and the atmosphere.
Natural gas often comes out of the well at a high pressure, for example, 1,000 pounds per square inch. The natural gas often undergoes some processing immediately downstream of the well, for example, water is often removed by running the gas through a dehydrator. A usual side effect of this processing is that it lowers the pressure of the gas downstream of the processing equipment relative to the pressure upstream of the processing equipment, typically by constricting the flow of the gas. Therefore, there is usually a pressure differential between the gas upstream of the processing equipment and the gas downstream of the processing equipment. In situations where there is no processing equipment, a similar pressure differential can be created merely by constricting the flow of the gas.
One embodiment of this invention receives gas from the upstream, higher pressure side of the processing equipment, uses it to power a pneumatic device and then exhausts the gas at a pressure high enough so that the gas can be reinjected at the downstream, lower pressure side of the processing equipment.
A feature of this invention is a pressure vessel strong enough to withstand the highest pressure found in the compressed gas system to which the pressure vessel is attached. The pressure vessel contains some or all of the pressure differential components of a pneumatic device, whereby, although the device operates at a high ambient pressure, such as 1,000 pounds per square inch, the differential pressure faced by the bodies and seals of the various components (not including those seals between the exterior and interior of the pressure vessel) is low, such as 25 to 30 pounds per square inch.
The pneumatic drive unit or pneumatic device can be any device that operates by converting the potential mechanical energy of a compressed gas into motion.
In one embodiment of this invention, the pressure vessel contains a valve means connected by suitable conduit to the relatively higher pressure compressed gas in the pipeline; to a pneumatic cylinder; and to the interior of the pressure vessel, such that the valve means can be actuated to restrict the flow of gas between two of the three conduits connected to the valve means, being between the conduit to the relatively higher pressure compressed gas in the pipeline and the conduit to the pneumatic cylinder; and between the conduit to the pneumatic cylinder and the conduit to the interior of the pressure vessel. The interior of the pressure vessel is connected by suitable conduit to the relatively lower pressure compressed gas in the pipeline, wherein the pressure in the pressure vessel is essentially the same as the relatively lower pressure compressed gas in the pipeline. The pneumatic cylinder contains a piston. The piston in the pneumatic cylinder is connected to a spring which acts to move the piston so as to evacuate the compressed gas from the cylinder. The piston in the pneumatic cylinder is connected to a means for actuating the valve means such that when the piston is at the top of its stroke, being the position of its stroke where the compressed gas is substantially evacuated from the pneumatic cylinder, the valve means is actuated to permit the compressed gas to flow from the pipeline to the pneumatic cylinder, and such that when the piston is substantially at the bottom of its stroke, being the position of its stroke where the pneumatic cylinder is substantially full of compressed gas, the valve means is actuated to permit the compressed gas to flow from the pneumatic cylinder to the interior of the pressure vessel. When the valve means is actuated to permit the compressed gas to flow from the pipeline to the pneumatic cylinder, the pneumatic cylinder fills with compressed gas and the piston moves to the bottom of its stroke. When the pneumatic cylinder is substantially full of compressed gas and the piston is at the bottom of its stroke, the valve means is actuated to permit the compressed gas to flow from the pneumatic cylinder to the interior of the pressure vessel and the spring pulls the piston to the top of its stroke evacuating the compressed gas from the pneumatic cylinder to the interior of the pressure vessel and thence to the relatively lower pressure portion of the pipeline. In this way the piston is made to move in a reciprocating motion. The piston can be connected to a variety of mechanical devices such that the reciprocating motion of the piston is used to drive the mechanical device.
The movement created when the pneumatic device is actuated by the compressed gas can be transferred to the exterior of the pressure vessel by a variety of mechanical means, such as by a reciprocating shaft passing through the vessel wall, or by a rotating shaft passing through the vessel wall.
With a shaft passing through the pressure vessel wall where there is a high pressure differential between the inside and outside of the pressure vessel, a shaft making a rotary movement is easier to seal than a shaft making a reciprocating movement. A feature of this invention is a means of changing a reciprocating movement of a piston into an oscillating rotary movement. In one embodiment, the piston is attached to one end of a chain, the first chain. The other end of the first chain is attached to the circumferential edge of a wheel. The wheel is concentrically mounted on a shaft. The shaft is connected to the walls of the pressure vessel so that it can only move rotationally. A second chain is also attached to the circumferential edge of the wheel. The second chain is attached to a spring. As the pneumatic cylinder fills with compressed gas the piston moves from the top of its stroke to the bottom of its stroke and pulls on the first chain which causes the wheel to rotate. This rotation of the wheel pulls on the second chain which stretches the spring. When the piston reaches the bottom of its stroke the compressed gas in the pneumatic cylinder begins venting to the interior of the pressure vessel. The spring attached to the second chain causes the wheel to rotate in the reverse direction to its previous rotation, which acts to pull the piston to the top of its stroke. When the piston reaches the top of its stroke, the compressed gas ceases venting to the interior of the pressure vessel, compressed gas starts flowing into the pneumatic cylinder and the cycle repeats itself. In this way the reciprocating motion of the piston is converted to an oscillating rotary motion of the shaft. The oscillating rotary motion of the shaft can be used to drive a mechanical device such as a pump by way of a pitman or crank arm, or some other suitable device.
A feature of an embodiment of this invention is the submersion of the components in oil or some other suitable liquid, which provides lubrication, minimizes wear and prevents corrosion.
In one embodiment of this invention, part or all of the components of the equipment which is driven by the pneumatic device are contained within the pressure vessel. In one embodiment, the equipment is a pump, and part or all of the components of the pump are contained within the pressure vessel. In this embodiment of the invention, a seal between the interior and exterior of the pressure vessel for a moving shaft is not necessary.
In one embodiment of the invention, the valve means is connected by suitable conduit to: the relatively higher pressure portion of the compressed gas system; to the pneumatic cylinder; and to an exhaust area. The exhaust area is an area in fluid contact with the relatively lower pressure portion of the compressed gas system. The exhaust area may be within the interior of the pressure vessel. However, in some cases it is preferable for the exhaust area to be outside of the pressure vessel. For example, in some cases the compressed gas contains liquids which can tend to precipitate out of the compressed gas and to remain in the pressure vessel. This can be avoided by venting the exhaust gases outside of the pressure vessel. In one embodiment, the exhaust gas is vented within the conduit connecting the pressure vessel to the relatively lower pressure portion of the compressed gas system, in such a way that liquids will tend to flow away from the pressure vessel. In this embodiment, the valve means is such that it can be actuated to restrict the flow of gas to between two of the three conduits connected to the valve means, being: between the conduit to the relatively higher pressure portion of the compressed gas system and the conduit to the pneumatic cylinder; and between the conduit to the pneumatic cylinder and the conduit to the exhaust area.
In one embodiment, the piston in the pneumatic cylinder is connected to a piston biassing means, typically a spring, which causes the piston to tend to move so as to evacuate the compressed gas from the cylinder. The piston in the pneumatic cylinder is connected to a means for actuating the valve means such that when the piston is at top of stroke, being the position of its stroke where the gas is substantially evacuated from the pneumatic cylinder, the valve means is actuated to permit the gas to flow from the relatively higher pressure portion of the compressed gas system to the pneumatic cylinder, and such that when the piston is substantially at bottom of stroke, the valve means is actuated to permit the compressed gas to flow from the pneumatic cylinder to the exhaust area. When the piston is at bottom of stroke, the valve means is actuated to permit the compressed gas to flow from the pneumatic cylinder to the exhaust area; and the piston biassing means causes the piston to move to top of stroke, evacuating the compressed gas from the pneumatic cylinder to the exhaust area and thence to the relatively lower pressure portion of the compressed gas system.
In one embodiment, the piston is connected to one end of a piston chain. The other end of the chain is circumferentially attached to a drive sprocket. The drive sprocket is concentrically mounted on a rotatable shaft passing through the wall of the pressure vessel. One end of a second chain, the return chain, is mounted circumferentially on the drive sprocket in opposition to the piston chain. The other end of the return chain is attached to: the return spring; or some other biassing means which puts tension on the return chain. The links of the piston chain and return chain are configured so as to engage with the sprocket teeth which are positioned around the periphery of the drive sprocket.
In use, as the pneumatic cylinder fills with compressed gas the piston moves from top of stroke to bottom of stroke, and pulls on the piston chain which causes the drive sprocket to rotate and which stretches the chainspring. When the piston reaches bottom of stroke, the valve means is actuated to permit the compressed gas in the pneumatic cylinder to vent to the exhaust area. The piston biassing means causes the piston to move to top of stroke. This reduces the tension on the return spring. The return spring, through the return chain, causes the drive sprocket to rotate in the reverse direction to its previous rotation. When the piston reaches top of stroke, the compressed gas ceases venting to the exhaust area, compressed gas starts flowing into the pneumatic cylinder and the cycle repeats itself. In this way the reciprocating motion of the piston is converted to an oscillating rotary motion of the shaft.
It will be clear to those skilled in the art that a variety of means for transforming the oscillating motion of the piston into a rotary motion could be employed, including but not limited to: a rack and pinion, and a swash plate drive.
The oscillating rotary motion of the shaft may be used to drive a mechanical device by converting the motion to non-oscillating rotary motion by means of a ratchet slip clutch and a flywheel.
It will be clear to those skilled in the art that with some pneumatic devices it is possible to connect the interior of the pressure vessel to the area of higher pressure in the compressed gas system whereby the work environment within the pressure vessel is in fluid contact with the area of higher pressure. With this configuration, the exhaust of the pneumatic device is connected to the area of lower pressure in the compressed gas system and the intake of the pneumatic device is in fluid communication with the interior of the pressure vessel.
Typically, when the pneumatic apparatus is used with a natural gas pipeline system it is necessary to use a differential controller to create the required pressure differential. The pipeline system may have a pressure differential which is either too small to drive the pneumatic apparatus or too large for the components of the pneumatic device to withstand. Differential controllers can take many forms. Typically they have a means for sensing the pressure upstream and downstream of a valve, these sensors being connected to a means for opening and closing the valve, so that the valve opening is constricted when the pressure differential is less than desired and enlarged when the pressure differential is greater than desired. In natural gas pipeline systems where the pressure differential naturally occurring in the system is too small, the differential controller is installed in line in the pipeline to create the necessary pressure differential. By contrast, in natural gas pipeline systems where the pressure differential naturally occurring in the system is too large, the differential controller is installed in line in the conduit between the pipeline system and the pneumatic apparatus to reduce the existing pressure differential.
It is clear that the pneumatic apparatus will only function when there is a pressure differential. In most compressed gas systems this pressure differential arises because the gas is flowing. The pressure differential disappears when the gas ceases to flow, even though the compressed gas system is still pressurized. In some applications, such as where methanol is being injected into a pipeline to act as an antifreeze, it is preferable that the methanol injection stop while the gas is not flowing. In other applications, such as where the pneumatic apparatus is being used to pump heated glycol through heat tracing positioned around above-ground portions of a pipeline, it is preferable that the pump continue to operate even though the gas is not flowing. If it is necessary to keep the pneumatic device operating whether or not the gas is flowing the conduit connecting the interior of the pressure vessel to the compressed gas system can be fitted with a bypass to a differential controller and thence to atmosphere.
In another embodiment of this invention, related to pressurising the work environment, where it is necessary to inject a liquid into a compressed gas, in a natural gas pipeline for example, enclosing the liquid in a container in which the liquid is under the same pressure as the compressed gas, and locating that container so that the outlet for the liquid is higher than the location where the liquid is injected into the compressed gas, results in a gravity-induced flow of the liquid from the container into the compressed gas. The liquid in the vessel can be pressurized to the same pressure as the compressed gas by many means, including locating the liquid container in a larger high pressure vessel containing the compressed gas, or making the liquid container itself a high pressure vessel with sufficient connections to the compressed gas to keep the liquid at the same pressure as the compressed gas and to permit a controlled flow of the liquid into the compressed gas. The flow of liquid into the compressed gas may be controlled by way of a metering valve or other similar device. The level of the liquid can be monitored with a high-pressure level sight glass. Liquid can be added to the liquid container by a variety of means, including, a high pressure pump if it is necessary to maintain the liquid at the same pressure as the compressed gas, or by gravity or other simple means if it is possible to isolate the liquid container from the compressed gas and bleed it down to atmospheric pressure.
According to one aspect, the invention consists of a pneumatic apparatus for using the pressure differential between an area of higher pressure and an area of lower pressure in a compressed gas system to drive equipment, the pneumatic apparatus comprising:
(A) a pressure vessel;
(B) a gas outlet in the wall of the pressure vessel, said gas outlet being in fluid communication with the interior of the pressure vessel;
(C) a pneumatic device, a portion of said pneumatic device being located within the pressure vessel, and said pneumatic device including an intake and an exhaust, wherein when the pneumatic device is being pneumatically actuated, the gas used to drive the pneumatic device passes into the pneumatic device through the intake and the exhaust gas is exhausted through the exhaust; and
(D) said pneumatic device exhaust being in fluid communication with the interior of the pressure vessel;
wherein if the gas outlet is connected by suitable conduit to the area of lower pressure whereby the interior of the pressure vessel is in fluid contact with the area of lower pressure and the pneumatic device intake is connected by suitable conduit to the area of higher pressure whereby the pneumatic device intake is in fluid contact with the area of higher pressure, then exhaust gas from the pneumatic device can flow to the area of lower pressure.
A portion of the equipment driven by the pneumatic apparatus may be located within the pressure vessel. The equipment driven by the pneumatic apparatus may be located outside the pressure vessel.
The pneumatic device may comprise:
(A) a pneumatic cylinder;
(B) a piston within the pneumatic cylinder, said piston defining a chamber with the pneumatic cylinder, said chamber changing in size as the piston moves within the pneumatic cylinder;
(C) a piston biassing means connected to the piston and causing the piston to tend to move to, and remain at, top of stroke, being the position of the piston where the chamber is the smallest;
(D) a three-port Y valve, wherein one port is connected by conduit to the chamber; one port is the pneumatic device intake and one port is the pneumatic device exhaust;
(E) a valve switch incorporated in the Y valve wherein when the valve switch is at a first position, gas can flow through the Y valve between the intake and the chamber, and when the valve switch is at a second position gas can flow through the Y valve between the chamber and the exhaust; and
(F) a linkage connecting the piston to the valve switch, wherein when the piston is substantially at top of stroke the valve switch is at the first position and when the piston is substantially at bottom of stroke the valve switch is at the second position,
whereby when the piston is at top of stroke, gas can flow from the intake to the chamber and when the piston is at bottom of stroke, gas can flow from the chamber to the exhaust.
The linkage may comprise:
(A) a rotatable member;
(B) a flexible member connected to the piston and attached to the rotatable member, whereby movement of the piston in the direction from top of stroke to bottom of stroke will cause the rotatable member to rotate in one direction;
(C) a rotatable member biassing means connected to the rotatable member and tending to cause the rotatable member to rotate in the opposite direction from that rotation caused by the movement of the piston in the direction from top of stroke to bottom of stroke;
(D) means for connecting the rotatable member to the valve switch.
The rotatable member may be attached to an output shaft. The output shaft may pass through the wall of the pressure vessel. The rotatable member may be a sprocket, said sprocket incorporating teeth, and the flexible member may be a chain, wherein the chain engages with the teeth. The rotatable member biassing means may comprise a spring, one end of the spring being connected to the drive sprocket. The means for connecting the rotatable member to the valve switch may comprise a switch spring.
The pressure vessel may contain a liquid. The liquid may be oil.
According to another aspect, the invention consists of a pneumatic apparatus for using the pressure differential between an area of higher pressure and an area of lower pressure in a compressed gas system to drive equipment, the pneumatic apparatus comprising:
(A) a pressure vessel; and
(B) a pneumatic device, a portion of said pneumatic device being located within the pressure vessel, and said pneumatic device incorporating an intake and an exhaust, wherein when the pneumatic device is being pneumatically actuated, the gas used to drive the pneumatic device passes into the pneumatic device through the intake and the exhaust gas is exhausted through the exhaust,
wherein if the pneumatic device exhaust is in fluid communication with the area of lower pressure and the pneumatic device intake is in fluid communication with the area of higher pressure, then exhaust gas from the pneumatic device can flow to the area of lower pressure.
The interior of the pressure vessel may be in fluid communication with the pneumatic device exhaust. The interior of the pressure vessel may be in fluid communication with the pneumatic device intake.
According to another aspect, the invention consists of a liquid injection apparatus for use with a compressed gas system comprising:
(A) a liquid container connected to the compressed gas system such that the interior of the liquid container is in fluid communication with the compressed gas system; and
(B) a conduit connecting the liquid container to an injection point on the compressed gas system,
wherein liquid can flow from the liquid container to the injection point.
The liquid injection apparatus may also comprise a pressure vessel, wherein: the liquid container is located within the pressure vessel, the interior of the liquid container is in fluid communication with the interior of the pressure vessel and the interior of the pressure vessel is in fluid communication with the compressed gas system. The liquid container may be located higher than the injection point on the compressed gas system.
The various features of novelty which characterize the invention are pointed out with more particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be made to the accompanying drawings and descriptive matter in which there are illustrated and described preferred embodiments of the invention.